1. Technical Field
The present invention relates to a method for manufacturing a piezoelectric vibration device generating a periodical electric signal by utilizing piezoelectric effect.
2. Related Art
A structure has been known in a surface acoustic wave device, which is one of the piezoelectric vibration devices. In the structure, an anodic bonding part is formed on a piezoelectric substrate having an interdigital transducer (IDT) electrode and a taking out electrode electrically conducted to the IDT electrode so as to surround the taking out electrode and the IDT electrode. A glass plate, which has a through hole formed at a part opposed to the taking out electrode of the piezoelectric substrate, is bonded to the piezoelectric substrate at the anodic bonding part. An external electrode, which goes to the taking out electrode of the piezoelectric substrate through the through hole of the glass plate, is formed by a film forming technique such as spattering. Refer to a first example of related art.
In the example described in the first example of related art, the bonding between a piezoelectric substrate and a glass plate is kept only by an anodic bonding part, while the sealing of a propagation surface, where a surface wave propagates, on the piezoelectric substrate and electrical conduction to the taking out electrode are kept by an external electrode formed on the taking out electrode of the piezoelectric substrate through a through hole of the glass plate. However, cracks or breaks are easily taken place in such external electrode due to stress easily concentrated at the boundary part of the through hole and the taking out electrode. Namely, the example described in the first example of related art has an unsolved problem in that it is difficult to improve reliability of airtight property inside a sealing or reliability of the electrical conduction between the taking out electrode and the external electrode.
A structure that can solve the problem is shown as follows: in a micro electro mechanical system (MEMS) switch in which silicon substrates are anodically bonded with a glass film therebetween, a through hole, in which an electrode electrically conducted to the MEMS switch is provided, is formed at the anodically bonded part; and the peripheral part of the through hole is also anodically bonded. Refer to a second example of related art. In the structure described in the second example of related art, even if an external electrode is formed through the through hole, the stress taken place at the external electrode can be lowered since the peripheral part of the through hole is anodically bonded to the silicon substrate having the MEMS switch.
JP-A-8-213874 is the first example of related art. JP-A-2005-125447 is the second example of related art.
In the example described in the second example of related art, the glass film and the silicon substrate are anodically bonded. For example, in a case where a glass film and quartz serving as a piezoelectric substrate are anodically bonded, it is necessary to insert metal between the quartz and the glass film since the quartz and the glass film cannot be directly anodically bonded. Namely, the anodic bonding is carried out by applying voltage between the glass film and the metal while the glass film and the metal are made contact with each other.
Accordingly, a piezoelectric vibration device having quartz as a piezoelectric substrate has an unsolved problem in that the metal at the anodic bonding part and the taking out electrode are electrically shorted if the structure described in the second example of related art is applied to the piezoelectric vibration device.